The present invention concerns a transmission unit for motor vehicles, a pulley used thereby, as well as a method for making such a pulley.
In particular, it concerns a transmission unit containing a continuous variable transmission, consisting of an ingoing shaft, a driven shaft, two pulleys situated on the ingoing shaft and the driven shaft respectively, and an endless transmission element provided between said pulleys, whereby the above-mentioned pulleys each consist of two pulley halves with conical contact surfaces which can be axially adjusted in relation to one another, such that the transmission ratio between the ingoing shaft and the driven shaft can be continuously altered.
It is known that with such a continuous variable transmission, it is possible to use a transmission element which consists of a lubricated belt which is provided with metal parts having contact surfaces which work in conjunction with the above-mentioned conical contact surfaces of the pulley halves. The metal parts are connected as such by means of flexible elements, such as cords or such.
The belt is lubricated by exposing the belt and/or the pulley halves to oil and/or a cooling liquid. This can be done in any way whatsoever. As described in European patent No. 0.574.085, this can be done for example by squirting the oil and/or the cooling liquid on the transmission element and/or the pulleys by means of one or several feed pipes.
New types of transmission elements have been developed recently whereby the contact surfaces of the parts are provided with a profiling which procure a thin-film lubrication. These profilings are made such that the above-mentioned parts locally penetrate deeper in the oil film situated between the parts and the pulley halves, so that a metal-on-metal contact is obtained locally, as a result of which the risk for the transmission element to slip under a heavy load is minimized.
Further, it is known that a new transmission element must always wear in, whereby the contact surfaces of the above-mentioned parts on the one hand, and the pulley halves on the other hand act on one another and adjust to one another as a result of minor wear, after which there will be practically no wear anymore, or at least the wear which is brought about afterwards is so minor that the life of the continuous variable transmission will exceed the normal life of the motor vehicle.
In transmission units which are equipped with the above-mentioned recent types of transmission elements, it was found, however, that there is often an unstable wear-in, whereby instead of the contact surfaces getting adjusted to one another, these surfaces start acting on one another more and more aggressively, and the roughness on these surfaces remains or even increases. As a result, the transmission unit is strongly subject to wear, so that the aimed life and quality are not achieved.
The invention aims a transmission unit with a transmission element which makes use of the principle of thin-film lubrication, but whereby the above-mentioned disadvantages are excluded with certainty.
To this end, the invention concerns a transmission unit of the type containing a continuous variable transmission consisting of an ingoing shaft, a driven shaft, two pulleys situated on the ingoing shaft and the driven shaft respectively, and an endless transmission element provided between said pulleys, whereby the above-mentioned pulleys each consist of two pulley halves with conical contact surfaces which can be axially adjusted in relation to one another, such that the transmission ratio between the ingoing shaft and the driven shaft can be continuously altered, whereby the transmission element consists of a lubricated belt which is provided with metal parts having contact surfaces which work in conjunction with the above-mentioned conical contact surfaces of the pulley halves, and whereby the contact surfaces of the parts have a profiling, in particular a profiling procuring a thin-film lubrication, characterized in that the conical contact surfaces of the pulley halves concerned are polished.
As use is made of a combination of a profiled contact surface on the above-mentioned parts and a polished contact surface on the pulley halves, the contact surface of the pulley halves is particularly smooth, and there are no two rough surfaces acting on one another, which finally has for a result that the profiled contact surface of the above-mentioned parts will always smoothly adjust to the contact surface of the pulley halves. This guarantees a stable wear-in.
The profile of the contact surfaces of the above-mentioned parts can be of any nature whatsoever and may for example consist of a punched profile, a corrugated profile or a profile formed of local recesses which are obtained for example by sandblasting the surface concerned.
The conical contact surfaces are preferably polished with a cloth with particles or with a polishing block. In particular, they are preferably polished by means of a rotating polishing movement. Thanks to this rotating polishing movement is obtained a very smooth surface. In the case where there are nevertheless roughnesses, they do not extend in the sense of rotation of the pulleys, which has for a result that, at the time of the wear-in, the roughnesses on the contact surface of the pulley halves can never co-operate with the profiling on the contact surfaces of the above-mentioned parts, and an unstable wear-in is once more counteracted.
Naturally, the invention also concerns a pulley for realizing the above-mentioned transmission unit, characterized in that it is provided with one or several conical contact surfaces which are polished.
The invention also concerns a method for realizing such a pulley, characterized in that, at the time of the final finishing, the conical contact surfaces are polished with a rotating polishing element.
A polishing element is hereby preferably used which has such a diameter that this polishing element covers the entire or almost entire radial length of the conical contact surface. As the entire radial length is covered at once, the creation of roughnesses is minimized.
It is also preferred that the polishing element, as it carries out a rotating movement around its own axis, is moved over the contact surface of the pulley half to be worked, such according to a circular path in relation to said pulley half.
According to a practical embodiment, the pulley half to be worked is driven in a rotating manner, and the rotating polishing element is represented to the rotating contact surface in a fixed place.